I'm glad I got dragged in to this thread.
With regard to discovery of matching rule support, today in LDAP
and X.500 there is NO discovery mechanism that a client can use for
determining whether a server supports a particular rule, any rule!
And, even if it were, it would be of significant value given the
distributed nature of LDAP/X.500 directories. That is, what good
is the discovery answer at the first server chains the subsequent
request using the feature to a second server?
These problems are generally address by a) having tri-state
filter logic (unsupported matching rules evaluate to Undefined,
which is not an error) and, in X.500, assertion relaxation
(or tightening).
Thanks, I am much relieved.